Porous activated carbon materials are promising products in the fields of catalysis and of the supercapacitors. They are also used in the adsorption and storage of the carbon dioxide and in the removal of pollutants such as arsenic from water.
Many porous materials based on carbon are known with different structures and morphologies and high surface areas. These materials are very convenient since they are cheap and show high thermal stability and high electrical conductivity.
There are three kinds of porous materials: 1) microporous materials having pores of diameter size less than 2 nm; 2) mesoporous materials having pores with diameter size in the range from 2 to 50 nm; 3) macroporous materials having pores with diameter size higher than 50 nm.
Such porous materials are generally produced by pyrolysis of biomasses such as mushrooms, corn, lignocellulose materials, fish scales and starch. These materials are promising as either supercapacitors or solid adsorbent materials for CO2.
In view of the interest generated by these porous products, synthesis methods have been studied and used.
In literature (J. Lee, J. Kim, T. Hyeon, Recent progress in the synthesis of porous carbon materials, Adv. Mater., 2006, 2073-2094) the following synthesis methods are described: 1) chemical and physical activation and their combination; 2) catalytic activation of carbonious precursors by means of metal salts or organometals, 3) carbonization of an aerogel polymer in drying super-critical conditions; 4) carbonization of polymer mixtures of pyrolizable and carbonizable polymers; 5) biomass pyrolysis.
These synthesis techniques allow mesoporous materials to be obtained.
The microporous materials are obtained by means of templates (J. Lee, J. Kim, T. Hyeon, Recent progress in the synthesis of porous carbon materials, Adv. Mater., 2006, 2073-2094) or through biomass pyrolysis.
In M. M. Bruno, G. A. Planes, M. C. Miras, C. A. Barbero, E. P. Tejera, J. L. Rodriguez, Synthetic porous carbon as support of platinum nanoparticles for fuel cellelectrodes, Molecular Crystal and Liquid, 2010, a porous carbon material from resin pyrolysis is described. Specifically a solution of a cationic surfactant, formaldehyde, resorcinol, Na2CO3 and deionized water was prepared, stirred and heated until the Krafft temperature of surfactant has been reached. After heating for 24 hours at 70° C. (atmospheric pressure), a brown polymer was obtained. After drying, the polymer was carbonized at 800° C. BET specific surface area was about 500 m2/g in the tested temperature. Another porous material was obtained by pyrolysis of polysiloxanes: polymethyl(phenyl)siloxane was crosslinked at 250° C. for 4 hours in air. The collected powder was pyrolyzed at 1250-1450° C. under vacuum Subsequently, the pyrolyzed samples were leached by hydrofluoric acid (HF) solution (40 vol %) at room temperature for 1 h under stirring and rinsed off with distilled water to remove residue HF. It was then dried at 110° C. The leaching treatment was repeated for 5 times to prepare porous carbonaceous materials until there was no distinct weight loss. The porous material obtained showed pore diameter in the range of 2-3.2 nm in the tested temperature range and BET specific surface area in the range of 650-1150 m2/g in the tested temperature range (L. Duan, Q. Ma, Z. Chen, The production of high surface area porous carbonaceous materials from polysiloxane, NEW CARBON MATERIALS, 2013, 235-240).
K. T. Cho et al (K. T. Cho, S. B. Lee, J. W. Lee, Facile synthesis of electrocapacitive nitrogen-doped graphitic porous carbon, J. Phys. Che., 2014, 9357-9367) used as precursor polyacrylonitrile. This precursor was oxidized at a temperature of 290° C. for one hour through heating at a rate of 2° C./min. After thermal treatment, the mass was ground and mixed to KOH. The mixture was heated to 700-800° C. for 1 or 2 hours under argon flux. The porous carbon so obtained after washing with HCl and rinsing with deionized water was dried in stove under vacuum at 120° C. The porous material so obtained showed a pore size distribution between 0.5 and 5 nm with a surface area above 3000 m2/g. Since the pore size distribution was between 5 and 50 {acute over (Å)}, this material resulted to be both microporous and mesoporous.
Many porous carbon materials deriving from biomasses showed high performances in many applications such as in the absorption of CO2 and in the removal of pollutants, for instance arsenic in the water.
Some porous materials were obtained by the hydrochar, i.e. from the hydrothermal carbonisation of Salix psammophila. The porours material so obtained is then activated under nitrogen through different temperatures for four hours at 4° C./min. After FTIR analysis the material resulted to have a condensate structure with BET SS Area of 300 m2/g and having micropores, mesopores and macropores.
Wang et al (H. C. Wang, B. L. LI, J. T. LI, X. B. Bian, J. Li, B. Zhang, Z. X. Wan, Direct synthesis of mesoporous from carbonization of hydroxypropyl-β-cyclodextrin/silica composite and its catalytic performance, Applied Surface Science, 2011, 4325-4330) used hydroxypropyl-β-cyclodextrin, which is a very expensive compound to synthesize a mesoporous material, by preparing a composite with silica. Specifically hydroxypropyl-β-cyclodextrin is dissolved in water and then added with tetrahydroxysilane (TEOS). The mass is then left for three days with continuous removal of ethanol and then heated at 100° C. for 12 hours. The final solid is then filtered and dried at 40° C. The material so obtained and consisting of HPCD/silica is then carbonised at 900° C. in nitrogen. After the carbonisation the material is treated with hydrofluoric acid in order to remove silica. Following to the thermal initial treatment BET SS areas between 500 and 1200 m2/g were obtained. The volume of the pores of the porous material were between 0.11 and 1.22 cm3/g, the total volume of the micropores was between 0.022 and 0.239 cm3/g.
A carbon porous material is valuable and finds easily applications if it shows a narrow diameter dispersion of the pores and if this feature is reproducible.
The carbon porous materials above described find application in many fields, specifically when they show reproducible and specific physical features such as constant sizes of the pores or the constant BET SS area.
The object of the present invention is hence to provide a carbon material having specific physical features.